1. Field of the Invention
This invention relates generally to video signal reproducing apparatus, such as, a video tape recorder (VTR) or the like, and more particularly is directed to a video signal reproducing apparatus which incorporates a time-base corrector.
2. Description of the Prior Art
When a video signal is reproduced by a video tape recorder or VTR, the reproduced signal is often supplied to a time-base corrector (TBC) in which a time-base of the reproduced signal is corrected for removing a jitter component therefrom.
A video signal reproducing circuit which incorporates a time-base corrector according to the prior art is shown schematically on FIG. 1 to include a rotary head drum assembly 1 around which a magnetic recording tape T is helically wrapped so that a magnetic head (not shown) provided in the drum assembly 1 will reproduce a video signal recorded in slant tracks on the tape T. The video signal reproduced from the magnetic tape T is shown to be supplied to a memory 2 which is included in a time-base corrector (TBC). The reproduced video signal is also supplied to an automatic frequency control (AFC) circuit 3 which generates a write clock signal W synchronized with the reproduced video signal which is written in the memory 2 in accordance with the write clock signal W. A standard or reference oscillation signal is supplied from an oscillator 4 to the time-base corrector memory 2 as a read clock signal R. Therefore, time-base fluctuations that may appear in the reproduced video signal due to a jitter component therein are removed from the video signal as the latter is read from the memory 2 in accordance with the standard read clock signal R. The resulting stable read-out video signal is supplied to an output terminal 5. The read clock signal R from the oscillator 4 is also supplied to a frequency divider 6 in which it is frequency-divided by a divisor n, whereupon the resulting frequency-divided signal is supplied to a servo control circuit 7 as a control signal therefor. The servo control circuit 7 effects servo control of a motor 8 for driving the rotary head drum assembly 1, and may also effect servo control of a capstan motor (not shown) by which the tape T is longitudinally advanced about the drum assembly 1.
When the video signal reproducing circuit is arranged as described above with reference to FIG. 1, the rotary head drum assembly 1 and the capstan for driving the tape are controlled on the basis of the read clock signal R for the memory 2 of the time-base corrector, and the writing cycle and the reading cycle of the memory 2 are approximately equal to each other. Therefore, it is possible to avoid or inhibit overtaking of the writing of the video signal in the memory 2 by the reading of the video signal from the memory, with the result that a stable time-base correction can be performed.
In the described video signal reproducing circuit according to the prior art, the reproduced video signal is written in the memory 2 as a composite video signal. In that case, the luminance and chrominance signals constituting the composite video signal must be kept in a stable interleaved relationship and, therefore, the described arrangement is, for the most part, utilized only in professional video tape recorders. However, the video signal reproducing circuit described with reference to FIG. 1 cannot be applied to a consumer or home video tape recorder of the type in which the chroma signal is down-converted in the recorded signal.
In the case of a video tape recorder of the down-converted chroma signal type, a chroma signal extracted from the reproduced video signal is demodulated to provide a base band signal which is then applied to a time-base corrector. However, in order to avoid deterioration of the chroma signal, it is desirable that the chroma signal be supplied directly to the time-base corrector without being first subjected to processing, such as, the described demodulation or the like.
On the other hand, if a reproduced video signal is supplied directly to a time-base corrector in the form of a high frequency signal reproduced from the magnetic tape so as to avoid deterioration of the reproduced signal by an intervening demodulation or other signal processing, the side band of the luminance signal included in the reproduced high frequency signal is expanded to a high band so that the operating frequency of the memory in the time-base corrector must be considerably increased, with a resulting increase in the scale of the circuit. Such a large scale circuit is difficult to provide in actual practice.
When the reproducing servo circuit 7 is controlled on the basis of the read clock signal R for the memory 2 of the time-base corrector, as in the prior art circuit shown in FIG. 1, if such memory 2 has a large storage capacity, for example, is a field memory so as to be capable of storing one field period of the reproduced video signal, the storage capacity of the memory is sufficient for ensuring that the read cycle of the video signal can be prevented from overtaking the writing cycle of the video signal in the memory 2. However, it is desirable to reduce the storage capacity of the memory 2 and thereby permit the scale of the video signal reproducing circuit to be correspondingly reduced.